1. Field of the Invention
The present invention relates generally to probe sequences and methods for detecting target nucleic acid molecules, and more specifically, to a probe for detecting antibiotic vancomycin-resistant enterococci (“VRE”) and methods thereof.
2. Description of the Related Art
Vancomycin-resistant enterococci (VRE) represent a serious problem for healthcare worldwide. Both vanA and vanB genes of enterococci have been found to be associated with the increased resistance. Transfer of the vanA and vanB antibiotic resistance genes to non-enterococcal species is also a growing concern. The vanA gene has been found in Corynebacterium, Arcanobacterium and Lactococcus species (Power et al., J. Antimicrobiol. Chemother. 36:595–606, 1995). Recently, Poyart et al. (Antimicrobiol. Agents Chemotherap. 41:24–29, 1997), reported an occurrence of a Streptococcus bovis clinical isolate with a VanB resistance phenotype. The gene was shown to be highly homologous to the prototype vanB gene from Enterococcus. Increased use of antibiotics has resulted in the emergence of vancomycin-resistant microorganisms, such as Enterococcus spp. and Staphylococcus spp. (Dutka-Malen et al., Antimicrobiol. Agents Chemother. 34:1875–1879, 1990).
Briefly, there are four phenotypes of enterococci that can be separated based on expression of constitutive and inducible resistance of the glycopeptides, vancomycin and teicoplanin (Leclercq and Courvalin, Clin. Infect. Dis. 24:545–556, 1997). Inducible resistance to high levels of vancomycin (MIC≧64 mg/l) and teicoplanin (MIC≧16 mg/l) is characteristic of the VanA phenotype. This type of resistance is plasmid mediated. The vanA gene has recently been found on mobile elements that can direct their own transfer from the chromosome of one Enterococcus strain to another. The VanB phenotype is described as inducible resistant to vancomycin with MIC of 4 mg/l to ≧1,000 mg/l but displaying susceptibility to teicoplanin. The vanB gene is transferable by conjugation in certain strains. The genes in the VanG phenotype produce constitutive resistance and occur in E. gallinarum and E. casseliflavis and E. flavenscens (Leclercq and Courvalin, supra; Navarro & Courvalin, Antimicrobiol. Agents Chemother. 38:1788–1793, 1994). Recently, a VanD phenotype has been reported and is characterized by moderate levels of vancomycin resistance and low level resistance to teicoplanin (cited in Leclercq and Courvalin, supra).
The majority of conventional methods for detection of glycopeptide resistant enterococci have drawbacks related to time, lack of specificity and sensitivity of detection. For example, detection of the glycopeptide resistant enterococci can be carried out by conventional susceptibility testing (broth and agar methods), but these techniques are slow, and automated detection is not recommended due to poor performance (Aarestrup et al., Antimicrob. Agents Chemother. 40:1938–1940, 1996).
Although the above methods can be used to detect VRE, there is an urgent need for a rapid and reliable method for simultaneously detecting the vanA gene and vanB genes from VRE, both in the hospital and community settings. The present invention provides compositions and methods for simultaneously and rapidly detecting the vanA and vanB genes. The present invention also provides other related advantages.